1. Field of the Invention
The present invention is directed to a method for removing solids or solids forming iron impurities from a solution. More particularly, this invention is a process for removing iron impurities from clear, high density brines used in oil or gas wells by precipitating the iron with zinc metal.
2. Description of the Prior Art
Clear, high density brines are used in oil well completions and workovers. They are also used as oil well packer fluids. Packer fluids are the fluids which are left in the annular space between the tubing and casing of oil wells. The primary purpose of these fluids is to balance the pressure in the well so as to prevent a well "blow out" without losing the fluid to the formation, and without damaging the formation as is done when solids-laden fluids are used. The densities required by these brines are determined by the well pressures and depths.
Oil well brines are usually prepared by blending different amounts and types of salt solutions to get the required density and clarity at the lowest cost. Such brines must be clear, that is, free of solids or solids forming materials such as iron. If iron is present in these brines, there may be an abnormally high color level and undesirable precipitates of compounds such as iron hydroxides. This precipitation phenomena may occur upon aging or sometimes upon blending various brines to obtain a desired density. Formation of green solutions containing a green precipitate of gelatinous ferrous hydroxide have been observed. Dark brown solutions may be caused by ferric ions.
These color related problems, caused by the presence of iron in brine, may have originated in the brine manufacturing process. Iron may have been present in the starting materials. Alternatively, the iron impurities may be "picked-up" during shipping, storing, handling or during the use of the brine "downhole" in a hot oil well.
It is economically advantageous to be able to treat new or used brine in a manner which removes iron impurities such that the treated brine can be used in an oil well. This treated brine may require the addition of other salts or salt solutions to obtain the desired density.